Note 5 - Investments in Affordable Housing and Alternative Energy Partnerships - Unfunded Commitments Future Estimated Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
2022	$ 49,206
2023	32,635
2024	17,722
2025	1,977
2026	1,489
Thereafter	4,623
Total unfunded commitments	$ 107,652	$ 103,060

Amount of scheduled funding for unfunded commitments in the next 12 months for affordable housing investments.

No definition available.

Name:	caty_AffordableHousingInvestmentsScheduledFundingForUnfundedCommitmentsInNext12Months
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of scheduled funding for unfunded commitments in the fifth fiscal year following the latest fiscal year for affordable housing investments.

No definition available.

Name:	caty_AffordableHousingInvestmentsScheduledFundingForUnfundedCommitmentsInYearFive
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of scheduled funding for unfunded commitments in the fourth fiscal year following the latest fiscal year for affordable housing investments.

No definition available.

Name:	caty_AffordableHousingInvestmentsScheduledFundingForUnfundedCommitmentsInYearFour
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of scheduled funding for unfunded commitments in the third fiscal year following the latest fiscal year for affordable housing investments.

No definition available.

Name:	caty_AffordableHousingInvestmentsScheduledFundingForUnfundedCommitmentsInYearThree
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of scheduled funding for unfunded commitments in the second fiscal year following the latest fiscal year for affordable housing investments.

No definition available.

Name:	caty_AffordableHousingInvestmentsScheduledFundingForUnfundedCommitmentsInYearTwo
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of scheduled funding for unfunded commitments after the fifth fiscal year following the latest fiscal year for affordable housing investments.

No definition available.

Name:	caty_AffordableHousingInvestmentsScheduledFundingForUnfundedCommitmentsThereafter
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Other liabilities from affordable housing unfunded commitments.

No definition available.

Name:	caty_OtherLiabilitiesFromAffordablehousingUnfundedCommitments
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant